1. Field of the Invention
The present invention relates to terrestrial Television networks. More particularly, it relates to the mobile set-top boxes for acquisition of digital terrestrial television programs in the presence of multiple transmission areas and to a mobile television receiver which can tune in diversity mode, and also in non-diversity mode.
2. Description of the Prior Art
Terrestrial television (also known as over-the-air, OTA or broadcast television) was the traditional method of television broadcast signal delivery prior to the advent of cable and satellite television. Although still in wide use, in some countries it is slowly becoming obsolete but in others, digital terrestrial has become popular. It works via radio waves transmitted through open space, usually unencrypted (commonly known as “free-to-air” television).
Terrestrial television broadcasting dates back to the very beginnings of television as a medium itself with the first long-distance public television broadcast from Washington, D.C., on Apr. 7, 1927. Aside from transmission by high-flying planes moving in a loop using a system developed by Westinghouse called Stratovision, there was virtually no other method of television delivery until the 1950s with the advent of cable television, or community antenna television (CATV). The first non-terrestrial method of delivering television signals that in no way depended on a signal originating from a traditional terrestrial source began with the use of communications satellites during the 1960s and 1970s.
In the United States and most of the rest of North America as well, terrestrial television underwent a revolutionary transformation with the eventual acceptance of the NTSC standard for color television broadcasts in 1953. Later, Europe and the rest of the world either chose between the later PAL and SECAM color television standards, or adopted NTSC.
In addition to the threat from CATV, analog terrestrial television is now also subject to competition from satellite television and distribution of video and film content over the Internet. The technology of digital terrestrial television has been developed as a response to these challenges. The rise of digital terrestrial television, especially HDTV, may mark an end to the decline of broadcast television reception via traditional receiving antennas, which can receive over-the-air HDTV signals.
In North America, terrestrial broadcast television operates on TV channels 2 through 6 (VHF-low band, known as band I in Europe), 7 through 13 (VHF-high band, known as band III elsewhere), and 14 through 69 (UHF television band, elsewhere bands IV and V). Channel numbers represent actual frequencies used to broadcast the television signal. Additionally, television translators and boosters can be used to rebroadcast a terrestrial TV signal using an otherwise unused channel to cover areas with marginal reception.
In Europe, a planning conference (“ST61”) held under the auspices of the International Telecommunications Union in Stockholm in 1961 allocated frequencies the Bands IV and V for the first time for broadcast television use. It also superseded the 1951 Plan (also made in Stockholm) which had first allocated Band II frequencies for FM radio and Band III frequencies for television.
Following the ST61 conference, UHF frequencies were first used in the UK in 1964 with the introduction of BBC2. Television broadcasting in Band III continued after the introduction of four analogue programmes in the UHF bands until the last VHF transmitters were switched off on Jan. 6, 1985. The success of terrestrial analogue television across Europe varies from country to country. Although each country has rights to a certain number of frequencies by virtue of the ST61 plan, not all of them have been bought into service.
By the mid 1990s, the interest in digital television across Europe was such the CEPT convened the “Chester '97” conference to agree means by which digital television could be inserted into the ST61 frequency plan. The introduction of digital television in the late 1990s and early years of the 21st century led the ITU to call a Regional Radio Communications Conference to abrogate the ST61 plan and to put a new plan for digital broadcasting only in its place.
By the year 2012, the EU will be entirely switched to digital terrestrial television broadcasting. Some EU member states have decided to complete this switchover as early as 2008 (e.g. Sweden). These digital terrestrial television broadcasting networks are multi-frequency networks (MFN). In this configuration, each given service is transmitted at a different frequency throughout the coverage area. Within each multiplex there are normally 8-12 services. Examples of services in the UK are BBC One, ITV1, Sky Travel and BBC Radio 1.
With this new age of digital terrestrial television networks, mobile television devices will not only become more popular, they will inherently require additional capabilities to provide the seamless flow of information to the end user without drop out or other interference that may be caused by traveling through multiple transmission areas. The new age of digital terrestrial networks will also require that mobile set-top boxes be created to receive mobile, digital television signals. In the past, Digital Video Broadcast-Terrestrial (“DVB-T”) could only be received by non-mobile set-top boxes, and as such could not be received in environments which required mobility. In the past, attempts to build mobile video device have utilized a traditional single DVB-T demodulator. Other attempts have utilized built-in car mobile video devices where the set-top box with a diversity demodulator is in the trunk, there are two antennas on the roof, and a large liquid crystal display (“LCD”) screen is built into the car. Thus, while diversity tuning has been known in the art especially for FM tuning, there has not heretofore been designed a diversity tuned, mobile set-top box.
However, diversity is not needed all the time. There are times during the operation of the system when signal reception is acceptable using only one receiver. The quality of these signals is subject to change as the unit moves. Moreover, scanning the frequency range allows the system to gather information about potential useful signals. This in turn allows the system to anticipate what channel to jump to when (and if) the current signal becomes degraded. This enhances user experience, as it provides for continuity of service as the uses watches a particular channel.